When two yeast cells mate, they must overcome the barrier of the cell wall and then coordinate leak-free fusion of their plasma membranes. Although proteins that peel away the cell walls have been identified, finding those involved in promoting the membrane fusion event has been difficult. Heiman and Walter used a proteomics-based approach to identify a protein termed Prm1. They developed a computer program to sieve a composite database of publised gene expression profiles of yeast cells, and they looked for predicted membrane proteins induced during mating. In experimental work, Prm1 was observed to localize at the tip of the mating projection, while in cells lacking Prm1, more than half of mating pairs failed to fuse even though their plasma membranes remained tightly apposed. It is not yet clear whether Prm1 is a ‘fusase’ or acts in support of such a molecule, but further study may clarify the details of the fusion process. — SMH